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WASHINGTON – Wisconsin Congressman Tom Petri shelled out almost $140,000 for legal representation last quarter as an ethics investigation continued into potential conflicts of interest over his advocacy for a military contractor in which he owns hundreds of thousands of dollars worth of stock.

The Fond du Lac Republican used campaign funds to pay Washington law firm Covington & Burling roughly $50,000 in May and $90,000 last month, according to campaign finance reports filed this week.

Petri, who has served in Congress for 35 years but announced in April he would not seek re-election amid the probe and a primary challenge, is being represented by a partner in the law firm's White Collar Defense & Investigations group, Robert Kelner.

Kelner declined to comment Wednesday. He is a prominent Republican attorney who has represented numerous clients facing congressional or law enforcement investigations.

They have included a consulting firm that failed to register as a lobbyist for former Libyan dictator Moammar Gadhafi, a campaign accountant who pled guilty to aiding an illegal contribution scheme for a Florida congressman in 2012, and a chief of staff to former Sen. John Ensign, R-Nev., who resigned in 2011 amid an ethics probe into his handling of an extramarital affair.

Petri said in a statement Wednesday that the House Ethics Committee approved his using campaign funds for his legal defense. He declined to comment on the status of the investigation or whether he has been cooperating with investigators. Petri has said previously that his attorney advised him not to discuss the matter.

"My lawyer advises me not to talk about it, ethics, because I might annoy the Ethics Committee," he said during a town hall meeting in April.

The congressman took the unusual step of asking for the investigation after the Gannett Washington Bureau and USA TODAY reported in February that he bought hundreds of thousands of dollars' worth of stock in Oshkosh Corp., a military truck manufacturer based in his district.

He then pressed colleagues on Capitol Hill and officials at the Pentagon to help the company retain a $3 billion military contract and escape Pentagon cuts. At the same time, the value of Petri's investment in Oshkosh grew 30 percent.

House ethics rules generally prohibit members of Congress from profiting personally from their official positions.

Petri said in April that he disclosed his interests in annual financial reports as required and that the investigation was "a work in progress."

"I believe that it will all work out in time," he said. "A lot of people own Oshkosh stock, I've worked for Oshkosh Company. It wasn't an effort to hype my stock."

The results of the probe may not be released publicly for at least another month. Preliminary investigations by the independent Office of Congressional Ethics typically take three months, and the House Ethics Committee can take another three months to decide whether to conduct a more comprehensive review and to release the initial findings. In Petri's case, that would put the timeline for release at the end of August.